1. Field of the Invention
The present invention relates generally to a signal processing apparatus, and more particularly to a signal processing apparatus capable of reducing a conversion error of a number of signal converters in which a number of circuits with the same construction and function, such as sample/hold circuits for driving a liquid crystal display, are arranged in parallel.
2. Description of the Related Art
Various devices have been made in conventional signal converters in which a number of circuits with the same construction and function are arranged in parallel, in order to reduce a conversion error of the signal converters. For example, various devices have been made in sample/hold circuits for driving a liquid crystal (LC) display, in order to reduce a conversion error arising in each sample/hold circuit.
For example, Jap. Pat. Appln. KOKAI Publication No. 6-54961 ("SAMPLE/HOLD CIRCUIT") and Proc. of 1993 VLSI Circuits Symp., pp. 118-119, Kyoto, Japan, May 1993 (A 700-MHz switched capacitor analog waveform sampling circuit) disclose methods in which a conversion error of a signal conversion apparatus comprising a number of such signal converters can be reduced by enhancing the precision of each signal converter.
A method called "dynamic element matching" or its improvements are known as other methods of reducing the conversion error. In these methods, when a plurality of single-functional circuits are combined to achieve one function, for example, when an n-number of current sources are combined to fabricate a D/A converter for expressing an n-number of gradients, one of the n-number of current sources is chosen to express gradient 1. Since any of the sources may be chosen, the probability of choice of one current source is equalized among all the sources. Thereby, errors of the current sources arising in the respective current sources are averaged and reduced to zero in total. Examples of this technique are a D/A conversion apparatus described in Jap. Pat. Appln. No. 4-140223 and a liquid crystal display driving apparatus described in Jap. Pat. Appln. KOKAI No. 2-189579.
The former prior art is useful in reducing the conversion error of the signal conversion apparatus. In the latter prior art, if sample/hold circuits are used to drive the LC display, the number of sample/hold circuits becomes several thousand in general, and large-scale peripheral control circuits are required. Furthermore, the shuffling mechanism of the signal processing devices is not effectively proposed, because the shuffling mechanism produces output noise. Thus, the feasibility of the latter prior art is very low.